Signet-ring stromal tumor of the ovary: an immunohistochemical and ultrastructural study with a review of the literature.

Signet-ring stromal tumor is a very rare type of ovarian neoplasm. Only ten cases of this tumor have been reported in the English literature. We report here an additional case of this type of tumor that arose from the left ovary in a 76-year-old woman. By light microscopy, the tumor was composed of small round and oval cells with cytoplasmic vacuolization and a typical signet-ring appearance, focally admixed with fibromatous tissue. Special staining revealed that the vacuoles of the tumor cells contained no lipid, mucoprotein, or glycogen. Interestingly, variously sized hyaline globule-like structures positive for periodic acid-Schiff (PAS) reaction with and without diastase digestion were present in the cytoplasm of tumor cells. Immunohistochemically, the tumor cells variously expressed several markers, including CD56, inhibin-alpha, alpha-smooth muscle actin (alpha-SMA), and progesterone receptor (PR), which have been identified in ovarian sex cord-stromal neoplasms. Ultrastructurally, the hyaline globule-like structures in tumor cells appeared to be lysosomes, and the vacuoles in the cells appeared to have resulted from pseudoinclusions of extracellular edematous matrix.